The present invention relates to a method for producing a bis(fluoroaryl)borane derivative such as a bis(pentafluorophenyl)borinic acid, which is useful as a polymerization catalyst, a polymerization co-catalyst, a catalyst for photopolymerization of silicone, an intermediate thereof, and an intermediate of a medicine or an agricultural chemical, for example.
Bis(fluoroaryl)borane derivatives such as bis(pentafluorophenyl)borinic acid, are compounds useful as polymerization catalysts, polymerization co-catalysts, catalysts for photopolymerization of silicone, intermediates thereof, and intermediates of medicines or agricultural chemicals, for example.
For instance, as a manufacturing method of bis(pentafluorophenyl)borinic acid, J. Chem. Soc (1965) 3933-3939 discloses a method in which water is added to bis (pentafluorophenyl) chloro borane in acetone at a temperature of xe2x88x9220xc2x0 C., then the acetone solution is concentrated, so that the bis(pentafluorophenyl)borinic acid is sublimated for purification, so as to be isolated. Furthermore, bis(pentafluorophenyl) chloro borane, which is a precursor of bis(pentafluorophenyl)borinic acid, is synthesized by reacting bis(pentafluorophenyl) dimethyl tin with boron trichloride. However, it is difficult to purify bis (pentafluorophenyl) chloro borane, because dimethyltin dichloride, which is a byproduct of the reaction, is sublimated when bis (pentafluorophenyl) chloro borane is isolated by distillation.
Moreover, J. Molecular Catalysis A: Chemical 144 (1999) 137-150 and WO 0037376 (2000) disclose that bis(pentafluorophenyl)borinic acid is prepared by heating tris (pentafluorophenyl)borane hydrate.
However, the method disclosed in the above-mentioned J. Molecular Catalysis A: Chemical 144 (1999) 137-150 discloses only how to manufacture bis(pentafluorophenyl)borinic acid, and fails to recite how to isolate bis(pentafluorophenyl)borinic acid from a reaction mixture, even though easy isolation and purification of the bis(fluoroaryl)borane derivative are necessary for industrial application of the bis(fluoroaryl)borane derivative as a catalyst or the like.
J. Molecular Catalysis A: Chemical 144 (1999) 137-150 recites only that it was confirmed by 19F-NMR that bis(pentafluorophenyl)borinic acid was prepared by adding water to a toluene-d8 solution of tris(pentafluorophenyl)borane so as to prepare tris(pentafluorophenyl)borane hydrate, then heating the solution of tris(pentafluorophenyl)borane hydrate.
Moreover, WO 0037476 (2000) discloses preparation of bis(pentafluorophenyl)borinic acid by heating tris (pentafluorophenyl)borane hydrate, and an isolation method of bis(pentafluorophenyl)borinic acid. Specifically, a toluene solution of tris(pentafluorophenyl)borane is heated up to 100xc2x0 C. Then, to the solution, a toluene solution containing water of 2.5 molar equivalent is dropped so that reaction is carried out at 100xc2x0 C. After the reaction, the solvent is concentrated in vacuo to dryness so as to isolate bis(pentafluorophenyl)borinic acid. However, it is recited that the bis(pentafluorophenyl)borinic acid obtained by this method contained boroxine by 5% as impurities. In short, this method has such a problem that the isolated bis(pentafluorophenyl)borinic acid has a low purity.
Moreover, that patent also discloses a method in which aluminum sulfate 18 hydrate is used instead of water. Specifically, aluminum sulfate 18 hydrate containing water of 1.77 molar equivalent vs. tris(pentafluorophenyl)borane is added to a toluene solution of tris(pentafluorophenyl)borane. After the solution is refluxed, insoluble aluminum sulfate is separated from the reaction mixture. A solvent of the filtrate is removed in vacuo. Toluene is added to the thus obtained residues. After stirring, the insoluble material is filtered through a G4 sintered-glass so as to be separated. The solvent of the filtrate is again removed in vacuo. Heptane is added to the residues. The solution is stirred and filtered so that a cake is obtained. Finally, the thus obtained cake is washed with heptane, and dried in vacuo so as to isolate bis(pentafluorophenyl)borinic acid. However, this method has such a problem that it is necessary to remove the byproduct aluminum sulfate and its process is so complicated.
Therefore, for industrial application of a bis(fluoroaryl) borane derivative, such as bis(pentafluorophenyl)borinic acid, as a catalyst or the like, there is a desire for a method by which the bis (fluoroaryl)borane derivative is easily isolated from a reaction mixture, and purified. Thus, the present invention, which is contrived in view of the foregoing problems, has an object of providing a method by which a bis(fluoroaryl)borane derivative can be produced, isolated, and purified with ease and at a low cost.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.
The inventor of the present invention, in order to attain the above-mentioned object, carried out an intensive study on a method for producing a bis(fluoroaryl)borane derivative such as bis(pentafluorophenyl)borinic acid. As a result, a molar ratio between tris(fluoroaryl)borane and a compound was studied, the tris(fluoroaryl)borane being represented by General Formula (1): 
(where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, at least one of R1, R2, R3, R4, and R5 representing the fluorine atom), the compound being represented by General Formula (2):
R0xe2x80x94MR6(R7)nxe2x80x83xe2x80x83(2)
(where each of R0, R6, and R7 independently represents one of a hydrogen atom and a hydrocarbon group, M represents an atom belonging to Group 15 or Group 16, and n represents 0 or 1). As a result, it was found that reaction rate was extremely decreased as the molar ratio was increased. Further, it was found that selectivity coefficient of the bis(fluoroaryl)borane derivative, which is a target compound, is decreased as the molar ratio is increased, the bis(fluoroaryl)borane derivative being represented by General Formula (3): 
(where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, at least one of R1, R2, R3, R4, and R5 representing the fluorine atom, and each of R6 and R7 independently represents one of a hydrogen atom and a hydrocarbon group, M represents an atom belonging to Group 15 or Group 16, and n represents 0 or 1), so that an optimal molar ratio between General Formulas (1) and (2) was found. Specifically, it was found that a bis (fluoroaryl)borane derivative having a high purity can be easily produced by having a molar ratio of 1:0.9 to 1:1.1 between the General Formulas (1) and (2). It was found that a hydrocarbon solvent is preferable as a reaction solvent, and that the bis(fluoroaryl) borane derivative can be isolated by concentrating a reaction mixture obtained by the reaction, more preferably by filtering the thus concentrated reaction mixture.
Specifically, in order to attain the above-mentioned object, a method of the present invention for producing a bis(fluoroaryl)borane derivative represented by General Formula (3): 
(where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, at least one of R1, R2, R3, R4, and R5 representing the fluorine atom, and each of R6 and R7 independently represents one of a hydrogen atom and a hydrocarbon group, M represents an atom belonging to Group 15 or Group 16, and n represents 0 or 1), includes the step of reacting tris (fluoroaryl)borane and a compound in a hydrocarbon solvent, in a molar ratio ranging from 1:0.9 to 1:1.1, the tris(fluoroaryl)borane being represented by General Formula (1): 
(where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, at least one of R1, R2, R3, R4, and R5 representing the fluorine atom), the compound being represented by General Formula (2):
R0xe2x80x94MR6(R7)nxe2x80x83xe2x80x83(2)
(where each of R0, R6, and R7 independently represents one of a hydrogen atom and a hydrocarbon group, M represents an atom belonging to Group 15 or Group 16, and n represents 0 or 1).
In order to attain the above-mentioned object, a method of the present invention for producing a bis(fluoroaryl)borane derivative represented by General Formula (3): 
(where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, at least one of R1, R2, R3, R4, and R5 representing the fluorine atom, and each of R6 and R7 independently represents one of a hydrogen atom and a hydrocarbon group, M represents an atom belonging to Group 5B or Group 6B, and n represents 0 or 1), includes the steps of mixing tris (fluoroaryl)borane and a compound in a hydrocarbon solvent, in a molar ratio ranging from 1:0.9 to 1:1.1, and reacting the tris(fluoroaryl)borane and the compound in a hydrocarbon solvent, while the hydrocarbon solvent is distilled off, the tris(fluoroaryl) borane being represented by General Formula (1): 
(where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, at least one of R1, R2, R3, R4, and R5 representing the fluorine atom), the compound being represented by General Formula (2):
R0xe2x80x94MR6(R7)nxe2x80x83xe2x80x83(2)
(where each of R0, R6, and R7 independently represents one of a hydrogen atom and a hydrocarbon group, M represents an atom belonging to Group 15 or Group 16, and n represents 0 or 1).
The method of the present invention for producing the bis(fluoroaryl)borane derivative includes reacting the tris (fluoroaryl)borane and the compound (hereinafter, just referred to as the xe2x80x9ccompound (2)xe2x80x9d) represented by General Formula (2) in the hydrocarbon solvent.
The tris(fluoroaryl)borane used as a starting raw material in the present invention is a compound represented by General Formula (1): 
(where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, at least one of R1, R2, R3, R4, and R5 representing the fluorine atom).
In the general formula, specifically, the hydrocarbon group for the substitutional groups represented by R1, R2, R3, R4, and R5 represents (a) an aryl group such as a phenyl group, (b) a straight or branched alkyl group containing 1 to 12 carbon atoms, (c) a cyclic alkyl group containing 3 to 12 carbon atoms, (d) a straight or branched alkenyl group containing 2 to 12 carbon atoms, and (e) a cyclic alkenyl group containing 3 to 12 carbon atoms. Examples of the alkyl group are, specifically, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a pentyl group, an isopentyl group, a t-pentyl group, a hexyl group, an octyl group, a cyclopentyl group, and a cyclohexyl group. An Example of the alkenyl group is, specifically, an allyl group.
Note that, the hydrocarbon group may further include a functional group including an atom that is inert to the reaction and process (purification) of the present invention, for example, a fluorine atom, a nitrogen atom, an oxygen atom, a sulfur atom, that is, an inert functional group. Examples of the functional group are a methoxy group, a methylthio group, an N,N-dimethylamino group, an o-anis group, a p-anis group, a trimethylsilyloxy group, a dimethyl-t-butylsilyloxy group, and a trifluoromethyl group.
In the general formula, the alkoxy group for the substitutional group represented by R1, R2, R3, R4, and R5 is represented by General Formula (A):
xe2x80x83xe2x80x94ORaxe2x80x83xe2x80x83(A)
(where Ra represents a hydrocarbon group).
In the general formula, the hydrocarbon represented by Ra specifically represents (a) an aryl group, (b) a straight or branched alkyl group containing 1 to 12 carbon atoms, (c) a cyclic alkyl group containing 3 to 12 carbon atoms, (d) straight or branched alkenyl group containing 2 to 12 carbon atoms, and (e) a cyclic alkenyl group containing 3 to 12 carbon atoms.
Examples of the alkoxy group represented by General Formula (A) are, specifically, a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxyl group, an isobutoxyl group, a sec-butoxy group, a t-butoxy group, a cyclohexyloxy group, an allyloxy group, and a phenoxy group.
Note that the tris(fluoroaryl)borane represented by the foregoing General Formula (1) is, for example, obtained by a method for reacting fluoroaryl magnesium halide and a borane compound.
Examples of the hydrocarbon solvent are (a) an aliphatic hydrocarbon solvent such as a saturated hydrocarbon solvent, an unsaturated hydrocarbon solvent, and an alicyclic hydrocarbon solvent and (b) an aromatic hydrocarbon solvent.
As the hydrocarbon solvent, the aliphatic hydrocarbon solvent is more preferable. Specifically, examples of the hydrocarbon solvent are 2,2-dimethylbutane, 2,3-dimethylbutane, 2,2,3-trimethylbutane, pentane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 2-methylpentane, 3-methylpentane, 2,2,4-trimethylpentane, 2,3,4-trimethylpentane, hexane, 2-methylhexane, 3-methylhexane, 2,2-dimehtylhexane, 2,4-dimethylhexane, 2,5-dimetylhexane, 3,4-dimehtylhexane, heptane, 2-methylheptane, 3-methylheptane, 4-methylheptane, 2,3-dimethylheptane, octane, nonane, decane, undecane, dodecane, tridecane, pentene, hexene, heptene, octene, cyclopentane, methylcyclopentane, ethylcyclopentane, cyclohexane, methylcyclohexane, 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane, ethylcyclohexane, cycloheptane, cyclooctane, cyclopentene, and cyclohexene. One of those hydrocarbon solvents may be used solely or more than two of those hydrocarbon solvents may be appropriately mixed and used. Moreover, commercial hydrocarbon solvents such as IsoparC, IsoparE, and IsoparG (any of them are Registered Trademarks) supplied from Exxon Corp. may be used.
It is preferable that the hydrocarbon solvent is substantially an aliphatic hydrocarbon solvent. For example, bis(pentafluorophenyl)borinic acid, which is a bis(fluoroaryl)borane derivative, is relatively soluble to the aromatic hydrocarbon solvent such as toluene. Thus, bis(pentafluorophenyl)borinic acid is obtained in a low yield when isolation of bis(pentafluorophenyl)borinic acid is carried out by filtration of a reaction mixture after concentration, in case the aromatic hydrocarbon solvent is used as a solvent. Because of this, it is necessary to have a step of concentrating to dryness the reaction mixture by distilling off the solvent, in order to have a high yield for isolation of the bis(pentafluorophenyl)borinic acid.
On the other hand, the bis(fluoroaryl)borane derivative has a low solubility for the aliphatic hydrocarbon solvent. Thus, in case the hydrocarbon solvent is substantially an aliphatic hydrocarbon solvent, it is possible to easily obtain the bis(fluoroaryl)borane derivative in a high yield by filtration of the bis(fluoroaryl)borane derivative after concentration of the reaction mixture.
Note that, in the present invention, the wording xe2x80x9cthe hydrocarbon solvent is substantially an aliphatic hydrocarbon solventxe2x80x9d means that a ratio of the aliphatic hydrocarbon solvent in the hydrocarbon solvent is within a range of 80% by weight to 100% by weight, and more preferably within a range of 95% by weight to 100% by weight.
The compound (2) used a starting raw material is a compound represented by General Formula (2):
xe2x80x83R0xe2x80x94MR6(R7)nxe2x80x83xe2x80x83(2)
(where each of R0, R6, and R7 independently represents one of a hydrogen atom and a hydrocarbon group, M represents an atom belonging to Group 15 or Group 16, and n represents 0 or 1).
In the general formula, the hydrocarbon for the substitutional groups represented by R0, R6, and R7, specifically represents (a) an aryl group such as a phenyl group, (b) a straight or branched alkyl group containing 1 to 12 carbon atoms, (c) a cyclic alkyl group containing 3 to 12 carbon atoms, (d) a straight or branched alkenyl group containing 2 to 12 carbon atoms, and (e) a straight or branched alkenyl group containing 3 to 12 carbon atoms. Examples of the alkyl group are specifically, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a pentyl group, an isopentyl group, a t-pentyl group, a hexyl group, an octyl group, a cyclopentyl group, and a cyclohexyl group. An Example of the alkenyl group is, specifically, an allyl group. Preferable as the substitutional group represented by R0 are a hydrogen atom or a methyl group and an ethyl group among the alkyl groups listed above.
In the general formula, a nitrogen atom or an oxygen atom is more preferable among atoms belong to Group 5b (Group 15 in the long periodic table) or Group 6b (Group 16 in the long periodic table) for the substitutional group represented by M.
Examples of the compound (2) are, specifically, water, methanol, ethanol, ammonia, methylamine, dimethylamine, ethylamine, and diethylamine. Among those, it is more preferable to use water as the compound (2). In case, water is used as the compound (2), bis(fluoroaryl)borinic acid is produced by hydrolysis of tris(fluoroaryl)borane.
As described above, in the present method for manufacturing, it is a preferable embodiment in which water is used as the compound (2) so as to carry out the hydrolysis, so that the bis(fluoroaryl)borinic acid will be obtained. Further, it is more preferable that the bis(fluoroaryl)borinic acid is bis(pentafluorophenyl)borinic acid.
By reacting the tris(fluoroaryl)borane with the compound (2) in the hydrocarbon solvent, the bis(fluoroaryl)borane derivative is obtained in the reaction mixture in which the bis(fluoroaryl)borane derivative is dissolved or suspended in the hydrocarbon solvent, the bis(fluoroaryl)borane derivative being represented by General Formula (3): 
(where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, at least one of R1, R2, R3, R4, and R5 representing the fluorine atom, and each of R6 and R7 independently represents one of a hydrogen atom and a hydrocarbon group, M represents an atom belonging to Group 15 or Group 16, and n represents 0 or 1).
A method of mixing Tris(fluoroaryl)borane and the compound (2) in the hydrocarbon solvent may be for example, a method of dissolving the tris(fluoroaryl)borane in the hydrocarbon solvent so as to prepare a solution, then adding the compound (2) into the solution, a method of adding the tris(fluoroaryl)borane and the compound (2) to the hydrocarbon solvent at the same time and mixing it, or a method of adding tris(fluoroaryl)borane in the hydrocarbon solvent in which the compound (2) has been added, and mixing it.
Tris(fluoroaryl)borane and the compound (2) are mixed in the hydrocarbon solvent preferably at a temperature in a range of xe2x88x92100xc2x0 C. to 300xc2x0 C., and more preferably at a temperature in a range of 0xc2x0 C. to 200xc2x0 C.
By mixing the tris(fluoroaryl)borane and the compound (2) in the hydrocarbon solvent, a complex of the tris(fluoroaryl)borane and the compound (2) is formed. The bis(fluoroaryl)borane derivative is obtained by heating the solution, which contains the complex.
For example, in case where (a) tris(pentafluorophenyl)borane ((C6F5)3B), in which all of R1, R2, R3, R4, and R5 in General Formula (1) are fluorine, and (b) water (H2O) in which of R0 and R6 are hydrogen, M is oxygen and n=0, are used, a complex of the tris (pentafluorophenyl)borane and water is formed in the hydrocarbon solvent. Then, the complex of the tris (pentafluorophenyl)borane and water is heated thereby producing bis(pentafluorophenyl)borinic acid ((C6F5)2BOH).
While the bis(pentafluorophenyl)borinic acid, which is a bis(fluoroaryl)borane derivative, is useful as a polymerization catalyst, a polymerization co-catalyst, and a catalyst for photopolymerization of silicone, (C6F5)B(OH)2, which is a byproduct of the reaction, reduces polymerization activity. Thus, it is preferable to suppress an amount of the byproduct as much as possible. Moreover, (C6F5)B(OH)2 tends to be dehydrated so as to be condensed depending on the condition of purification, and may produce boroxine, which is a trimer. This boroxine is also not preferable as impurities. Thus, the amount of the boroxine produced need be suppressed as much as possible. Moreover, tris(pentafluorophenyl)borane, which is a raw material, is not preferable as impurities. Thus, it is necessary to have the conversion as high as possible.
For this reason, the reaction of the tris(fluoroaryl) borane and the compound (2) is carried out in the molar ratio ranging from 1:0.9 to 1:1.1 so that the conversion of the tris(fluoroaryl)borane will be high and the production of (C6F5)B(OH)2, the byproduct of the reaction, will be suppressed, thereby obtaining (C6F5)2B(OH), the target compound with a high yield.
In the reaction of tris(fluoroaryl)borane and the compound (2) in the hydrocarbon solvent, it is more preferable that the hydrocarbon solvent is used in such an amount in which concentration of the tris(fluoroaryl) borane is within a range between 0.1% by weight and 80% by weight, and it is further preferable that the hydrocarbon solvent is used in such an amount in which concentration of the tris(fluoroaryl)borane is within a range between 1% by weight and 30% by weight. It is more preferable that the reaction is carried out at a temperature in a range from 0xc2x0 C. to 300xc2x0 C., and it is further preferable that the reaction is carried out at a temperature in a range from 50xc2x0 C. to 200xc2x0 C. Reaction time may be appropriately set in accordance with combination of the tris(fluoroaryl)borane and the compound (2) and/or the temperature at which the reaction is carried out.
The bis(fluoroaryl)borane derivative, which is the target compound, is obtained by the reaction. The reaction mixture obtained by the reaction contains a fluorobenzyl compound, which is by-produced together with the bis (fluoroaryl)borane derivative. For example, in case tris (pentafluorophenyl)borane and water are used as the raw materials, pentafluorobenzen (C6F5H) is contained in the reaction mixture, together with bis(pentafluorophenyl)borinic acid, which is the target bis (fluoroaryl)borane derivative.
It is preferable that the reaction is carried out while the hydrocarbon solvent is distilled off. With the arrangement in which the reaction is carried out while the hydrocarbon solvent is distilled off, it is possible to easily remove the pentafluorobenzen, which is by-produced in the reaction.
The reaction mixture obtained by the reaction is concentrated, and if necessary the thus concentrated reaction mixture is cooled, so as to precipitate, from the reaction mixture, crystal of the bis(fluoroaryl)borane derivative, which is the target compound.
As to conditions for the concentration of the reaction mixture, it is more preferable that the reaction mixture is concentrated until concentration of a compound derived from tris(fluoroaryl)borane originally added in the solution reaches a range between 5% by weight and 100% by weight. It is further preferable that the reaction mixture is concentrated until the concentration of the compound derived from tris(fluoroaryl)borane originally added in the solution reaches a range between 10% by weight and 80% by weight. As to pressure during the concentration, there is no particular limitation. Thus, the pressure during the concentration may be ordinary pressure (atmospheric pressure) or reduced pressure.
It is more preferable that a temperature to which the reaction mixture is cooled down for precipitating the crystal, is within a range from xe2x88x9250xc2x0 C. to 50xc2x0 C. It is further preferable that the temperature to which the reaction mixture is cooled down for precipitating the crystal, is within a range from xe2x88x9220xc2x0 C. to 30xc2x0 C. Duration for concentrating the reaction mixture and duration for cooling the reaction mixture may be appropriately set in accordance with an amount of the reaction mixture or the like condition. By filtering out the crystal thus precipitated, it is possible to easily isolate bis(fluoroaryl)borane derivative from the reaction mixture.
It is preferable that the thus obtained bis(fluoroaryl) borane derivative has purity of 98% or more. For example, bis(pentafluorophenyl)borinic acid having a high purity is useful as a polymerization catalyst, a polymerization co-catalyst, and a photopolymerization catalyst for silicone, because the bis(pentafluorophenyl)borinic acid having a high purity has not a large amount of impurities, which reduces polymerization activity.
It is possible to easily isolate the bis(fluoroaryl) borane derivative by concentrating, cooling, and filtering the reaction mixture as described above. Moreover, a cake obtained by filtering the reaction mixture is washed with a poor solvent, if necessary. In this way, it is possible to remove the byproduct and the like from the cake. By doing this, it is possible to isolate and purify the bis(fluoroaryl) borane derivative with ease and at a low cost.